This invention relates generally to the treatment of sewage and more particularly to an improved method and apparatus for aerobically treating wastewater.
In the past, it has been common for septic tanks to be used in places remote from public sewers. Use of the septic tank and its anaerobic process often results in the emission of offensive odors and additional problems such as the tendency for partially treated sewage to discharge into the soil and to contaminate ground water. Maintenance and periodic cleaning of septic tanks have been difficult, time consuming and unpleasant tasks.
Although wastewater has been aerobically treated in multi-compartmented septic type tanks, such tanks have also been less than satisfactory in a number of respects. The principal difficulty has been to achieve thorough mixing of the waste materials with oxygen and aerobic bacteria, which is essential if the solid wastes and organic materials contained in the wastewater are to be effectively treated. Existing tanks do not achieve sufficient mixing and aeration to prevent escape of substantial amounts of solid waste materials and dissolved organic substances into the drainage field. In addition, the inefficient manner in which oxygen is supplied necessitates that the aeration device operate for long periods, thereby consuming large quantities of power.
Another major problem with some existing aerobic treatment tanks results from the lack of aeration of the primary compartment into which the wastewater flows. Offensive odors are emitted from the primary compartment if it is not adquately aerated so that the aerobic organisms can break down the odor causing the wastes. The primary compartment may function as a small septic tank with the limitation of septic tanks. Existing tanks may also provide a number of separate treatment compartments of various sizes, thus complicating the structure and significantly increasing the costs. Further, the primary compartment is usually too small to store large quantities of sludge or solids from the incoming sewage, and the capacity of the system suffers accordingly.
Most home treatment systems of the aerobic type rely on gravity flow of sludge from the clarification zone back into the aeration zone. The resultant accumulation of large amounts of sludge in the clarification zone inherently results in at least some of the sludge being carried out of the tank by the discharging liquid. Perhaps even more importantly, the accumulated sludge tends to clog or block the gravity return path of the sludge which is the same path the liquid flowing from the aeration zone to the clarification zone must travel. The liquid flow thus opposes the return flow of sludge such that both flows are impeded, resulting in sludge being entrained by the liquid and swept into the clarification zone then into the tank discharge.
Systems which treat wastewater in batches, as exemplified by the Kelsey U.S. Pat. No. 3,834,536, are inefficient as compared to flow thru type system tanks wherein the outflow rate approximates the inflow rate to the systems. (Rates of inflow as outflow affected by large tank volume, baffle, etc.) In a batch process, there is a rather high rate of discharge from the tank at times when there may be no incoming liquid and, conversely, there is no discharge at other times when there may be a substantial quantity of wastewater entering the tank. Consequently, there is no consistency of the flow rates and aerobic treatment as occurs in the flow thru type tank. Moreover, the relatively high discharge rate that periodically occurs causes entraining of solid wastes by the outflowing liquid and thus carries considerable quantities of waste material out of the tank and into the discharge or drainage field.
Aside from their ineffectiveness in treating sewage, systems such as that of the aforementioned Kelsey patent are overly complicated in that two or more pumps are required. Also, complex valve arrangements and electrical controls are necessary to achieve the intended manner of intermittent or batch operation. Another problem with this type of system is that sludge is able to build up in substantial quantities in the settling zone from which liquid is discharged directly to the drainage field. Because there is a pump disposed in the aeration zone, special structures such as wire cages or similar costly devices are necessary in order to prevent rags and heavy solids from reaching the pump and possibly jamming or otherwise damaging it.
In view of these and other problems associated with existing systems for treating sewage, it is apparent that there is a need to treat wastewater in a more efficient and effective manner. It is the primary goal of the present invention to meet that need.
More specifically, it is an important object of the invention to provide a method and apparatus for treating wastewater wherein solids that enter the clarification chamber settle out and are positively pumped back into the aeration chamber. Accordingly, there is no substantial build up of sludge in the clarification zone and the liquid that is discharged to the drainage field is free of solid waste. In addition, the drawbacks of gravity return are avoided.
Another important object of the invention is to provide a method and apparatus for treating wastewater which achieves thorough mixing and aeration of the waste material in the aeration chamber. The high degree of mixing and the efficiency of the aeration brings the oxygen and aerobic bacteria into intimate contact with the organic waste materials, thereby enhancing the aerobic process which oxidizes and breaks down the wastes. Energy is conserved because the aeration device needs to operate for only short periods due to the efficiency of the aeration.
Still another object of the invention is to provide a method and apparatus of the character described wherein solids and organic materials are able to pass into the settling or clarification zone in only small amounts. This maintains the clarification zone in a substantially solid free condition so that only clear, odorless liquids are discharged to the tile field. Any solids that do enter the clarification zone tend to settle to the floor where they are positively pumped back into the aeration chamber retained in the system and subjected to further aerobic treatment.
A further object of the invention is to provide a method and apparatus of the character described in which the solid waste materials are saturated with air as they are being pumped back into the aeration zone.
An additional object of the invention is to provide a method and apparatus of the character described wherein the sludge return path from the settling zone to the aeration zone is separate from the liquid flow path from the aeration zone to the settling zone. Unlike gravity flow systems, the flow paths are separate and are thus not counter to one another. As a result, there is no possibility of the flows impeding one another or of the returning sludge being swept into the settling zone by counterflowing liquid.
A still further object of the invention is to provide a method and apparatus of the character described wherein a flow thru treatment system is employed. Liquid is tested and discharged over a more continuous time frame with outflow from the system occuring anytime there is an inflow of wastewater. The advantages of the batch type process are thus avoided.
Yet another object of the invention is to provide a sewage treatment system having a tank divided into only two compartments and presenting a large aeration chamber which is completely and efficiently aerated and mixed. In addition, the primary (aeration) compartment is adequately sized to store accumulated solids from treated waste.
A further object of the invention is to provide a sewage treatment system that employs only a single pump and requires no complicated valves or complicated electrical controls. The pump is disposed in the settling zone where it is isolated from rags and heavy solids without the need for cages or other special structures.
An additional object of the invention is to provide a sewage treatment system in which the flow patterns in the aeration and settling chambers plus transfer devices between these chambers impede the passage of solids through the system.
Still another object of the invention is to provide a sewage treatment apparatus which is simple and economical to construct and which is particularly suited for the treatment of household wastes.
Other and further objects of the invention, together with the features of novelty appurtenant thereto, will appear in the course of the following description of the drawings.